AbstractPolymerization of epichlorohydrin (ECH) in the presence of diols, catalyzed by Lewis or protic acids, proceeds by activated monomer mechanism (AMM), i.e., by subsequent additions of protonated monomer molecules to the terminal hydroxyl groups of the growing chain. As opposed to the typical active chain end mechanism, side reactions, including cyclization, are strongly suppressed in the polymerization by AMM and well‐defined linear product are obtained. It follows from kinetic considerations, that in order to achieve the high contribution of AMM, the reaction should be carried out at low instantaneous concentration of monomer, and this can be accomplished by slowly adding ECH to the reaction mixture. Using this approach, polyepichlorophydrin diols have been prepared in the M̄n ∼ 2500 products with DPn = [M]0/[I]0 can be obtained practically free of cyclic by‐products with the yields approaching quantitative. Polyepichlorohydrin diols obtained by AM polymerization are strictly bifunctional, regular head‐to‐tail polymers containing mainly (≥ 95%) secondary hydroxyl and groups.